Bikes have certainly evolved over the past few years. Remember when 29er bikes were only for XC, 27.5 wheels really didn't exist, and your trail bike had 2.2 inch wide tires? Within the last 5-6 years, trail and XC bikes have seen a huge change not only in geometry but what parts bike brands are choosing to spec from the factory.
Some of this is due to the availability of the new “trail” category; getting wider tires in lighter weights, also many people have realized that adding a few pounds doesn't hurt their normal riding much at all. This goes the same with geometry.
Riders who used to ride 4 hour days typically leaned towards light bikes with steep headtube angles, long stems, and skinny tires. Now it wouldn’t be surprising to see a 30 lb, 170mm bike doing big rides. One of the main reasons for that is because bike geometry has changed to suit riders who like to do both, pedal up and rip down. This is most likely a result of the EWS gaining a huge following and riders having to pedal the transfers (liaisons) and then ride DH style tracks on the way down. Racers want a bike that can make it to the top without pedaling a DH bike tank but can also handle the rough chunder on the way down.
Let's first start with some of the major changes trail bikes have had for geometry. Probably the most talked about is head tube angle. This is the angle of the head tube or steering axis, to the ground, or a horizontal plane. Head tube angle is one of the most influential aspects of frame geometry and can really take a bike from an XC weapon to a trail slayer with only a few degrees of tweaking.
Just a few years ago, a trail bike would have a 69-67-degree head tube angle. Nowadays, you can easily find a selection of trail bikes with 66.5-degree head tube angles, while some slacker bikes might even use 64-degree head tube angles. While only being a few degrees different, this can be one of the most noticeable handling differences.
Going slacker can have its benefits. When the terrain gets steep, you have better control. The downside is at slow speed, up or downhill, you do not have as great control. I think where bikes are now, we have found a sweet spot for head tube angles and handling characteristics. Downhill bikes, for instance, use anywhere from 62-63 degree head tube angles on average, and these bikes are not as efficient in slow tech terrain.
Next, I’m going to talk about reach and wheelbase, as they go hand in hand. Reach is the horizontal measurement from a straight line (Y-axis) up from the center of the bottom bracket to the center of the headtube. The reach is then the measured length of the X-axis. There will be images to help you understand as well.
Over the last few years, especially in the last two, the reach on most mountain bikes has got much much longer. Wheelbase is rather easy as it’s the measurement from one axle to the other. When the reach gets longer so does the wheelbase (assuming the head tube angle and fork offset stay the same). A longer reach can be very helpful to have room to move around. Also, it helps if you prefer running a shorter stem and having a quicker turning front end.
A longer wheelbase keeps the bike in control on high-speed sections. The bike becomes less twitchy and can help smooth out some rough sections. This longer wheelbase combined with the slacker headtube angle creates a much different riding bike than what we have been riding before this, making the bike much better at high speeds.
Reach numbers for 2018 and 2019 have grown an insane amount from years past. What is now called a size Large might have been considered an XL just a few years ago. And it’s possible that some of those longer bikes didn’t even exist at the time. Brands like Mondraker, GeoMetron, and Pole were some of the first to bring these longer frame designs intended to be used with shorter stems into the industry.
While a long reach has some great benefits to being more stable at high speed, there are also some downsides. Running a shorter stem has become very common lately, however it will allow you to get less weight over your front wheel which can often lead to less traction. Another downside is that it will shift your center of mass farther back on the bike which will make you set up your front and rear suspension slightly differently to keep your bike balanced. Lastly, a long bike is very stable but also more difficult to move around. If you are moving to a bike with a longer reach, it will take some time to be able to comfortably jump, turn, and bunnyhop the bike.
One of the last bits as far as what can help a bike climb better but not affect the way it handles downhill is the seat tube angle. Seat tube angle is measured very similarly to the headtube angle; from the ground or horizontal axis to an imaginary line drawn from the center of the bottom bracket to the center of the seat. That measurement is referred to as the effective seat tube angle.
The actual seat tube angle is measured again from the ground but to the actual seat post on your bike. This measurement tells you less about the climbing characteristics of the bike because it can change from one bike design to another without changing the effective seat tube angle. For example, older bikes may have had an effective seat tube angle anywhere from 68 (very slack), to 74 (steep).
Newer bikes may range anywhere from 72 degrees to 77 degrees and possibly even steeper. This helps you sit in a much more upright position with your feet, knees, and hips on top of the bottom bracket, helping you pedal more efficiently.
As a previous XC racer, this is one of my favorite newer trends. Previously, trail bikes always felt like something like pedaling a couch. Along with a longer reach, a steeper effective seat tube doesn't really change anything but your pedaling position. To me, there really aren’t any drawbacks to this unless the reach does not also increase. If that is the case, you will become much closer to the handlebars, ending up too cramped to climb comfortably.
There are a few more geometry features that have changed. Chainstay length has become shorter, helping you get around tight corners easier. The chainstay length is measured with a straight line from the center of the bottom bracket to the center of the rear axle.
If you have been following along then you have noticed that your weight has been moving more and more forward with each change. If the chainstay length remained the same, the bike would be too long and the rear wheel would be too far behind you, handling would feel like towing a boat.
A shorter chainstay length helps keep the weight more centered between the wheels and also helps maneuverability with the longer wheelbase and slacker headtube. A lot of people will argue that shorter chainstays are more fun to ride but are less stable, which seems to be contradictory to what is trying to be done with head tubes getting slacker and reach getting longer.
Increasing the reach while decreasing the chainstay length does help center your weight between the wheels however your point of contact is still ultimately going through your pedals and your grips. Moving your center of mass farther forward does help with front end traction but can often lead to less rear wheel traction.
Bottom bracket heights have also changed, becoming much lower, also lowering your body weight into the center of the bike. Many riders have said that bottom brackets are becoming too low, but if you are looking to have a bike really shine on the descents, a lower bottom bracket will add some stability having a lower center of gravity.
One company, Transition bikes, have combined much of these design features into their latest bikes calling it SBG (speed balanced geometry). One thing they also did was reduce fork offset to help front-end handling with a slacker head tube. We have covered both SBG and fork offset in other blogs, so we won't get too in depth here but essentially reducing fork offset will increase the trail measurement of the bike. When going slack, you can often get a front end “tuck” since the wheel is so far in front of the body. Reducing the fork offset will bring the wheel in closer, further increasing the balance on the bike.
While each of these is measured individually, it really does take the combination of all to make the bike a new creature. In our video, Jeff rode his 2018 Yeti SB4.5 (that was released in 2016) and compared it to his 2018 Transition Smuggler (released in 2018).
The SB4.5 sports relatively new geometry while the Smuggler is rocking the new and most extreme geometry. While the SB4.5 certainly can’t be considered ancient frame geometry, there are some traits that are older while the Smuggler fits all of the new geometry concepts. There are some major improvements from the SB4.5 that really help it handle better when the trail points downwards.
Everything I mentioned above has been thrown at the Smuggler from a slacker Headtube Angle, longer Reach, longer Wheelbase, a shorter Chainstay length, lower BB height, and a reduced offset fork.
On the trail, there are some noticeable differences, even though you can go out and have a blast on both bikes! Now, if Jeff rode the same trail on his Smuggler and also had a first gen Santa Cruz Tallboy, I bet he would notice some major differences. Mostly while descending, the headtube angle is over 4 degrees slacker and wheelbase is so much longer it might not even fit in the same zip code.
The Tallboy would be much twitchier, wouldn’t handle steep terrain with the same confidence the Smuggler does, and you would feel the shorter wheelbase in everything from cornering to high-speed sections. When comparing the Smuggler to the Tallboy, the differences could absolutely change your experience coming down your favorite descent.
Do you need to upgrade your bike to still have fun? No. But could you improve your riding with a bike that has this newer style of geometry? I would say it's very possible. It's still very new, but with big brands starting to jump on this trend, the testing is there and it's been proven. The last two Enduro World Series races were dominated by Richie Rude on a 2019 Yeti SB150, a bike with radical geometry features, proving these bikes can be ridden fast!